Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $239.86   9.561%   $262.793   $262.79   $262.80   $262.80  
  Purchase #2 $47.80   12.727%   $53.8835   $53.88   $53.90   $53.90  
  Purchase #3 $33.97   13.690%   $38.6205   $38.62   $38.60   $38.60  
  Purchase #4 $165.47   9.469%   $181.1384   $181.14   $181.15   $181.10  
  Purchase #5 $234.26   8.252%   $253.5911   $253.59   $253.60   $253.60  
  Purchase #6 $177.42   13.705%   $201.7354   $201.74   $201.75   $201.70  
  Purchase #7 $58.51   4.314%   $61.0341   $61.03   $61.05   $61.00  
  7 purchase totals = $957.29       $1,052.7960   $1,052.79   $1,052.85   $1,052.70